Most devices are actually black but Apple tends to make white products (even if they do offer other colours, it's the white version in their ads) to differentiate themselves from other products.

Because Apple puts a strong emphasis on marketing, a device that has white casing is seen as new and more advanced than other products. So when companies are promoting a new technology they will tend to make it white to piggy back on Apple's extensive marketing.

I mean look at that photo of that robot. They'd probably need to round out the edges a little more to make people feel like it's something that Apple would make but there is some degree of association there.

There's probably some influence from science fiction too, but the root cause of the aesthetic of the robots in things like the Portal games can probably be traced back to Apple as well. I don't recall robots in science fiction looking this way until after Apple went this direction in their product design.